1. Field of the Invention
The present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus for controlling an image forming operation in accordance with a current detection state of a main charger in a laser printer, copying machine, or the like employing an electrophotography process.
2. Description of the Related Art
As a conventional image forming apparatus, a so-called laser printer is developed, which has a cycle of printing by scanning exposure by a laser beam and an electrophotography process. Such a laser printer comprises a drum-like photoconductive body. A main charger, exposure unit, developing unit, transfer charger, peeling charger, discharger (discharging lamp), and the like are sequentially arranged around the photoconductive body along its rotating direction. The surface of the photoconductive body is uniformly and negatively charged by the main charger, and is then reversely exposed by a laser beam in the exposure unit. Thus, an electrostatic latent image in which only an information region is substantially at 0 V is formed. The latent image is reversely developed by a negatively charged toner in the developer, thereby visualizing the latent image. As a result, a toner image is formed. The toner image is transferred onto a paper sheet by the transfer charger having a polarity (positive polarity) opposite to that of the toner. Thereafter, the paper sheet is peeled from the photoconductive body by the peeling charger. In addition, the latent image on the photoconductive body is discharged (erased) by the discharger, thus completing one cycle.
After the image formation cycle is completed, the main charger, transfer charger, and peeling charger are sequentially turned off at predetermined timings. After the peeling charger is turned off, rotation of the photoconductive body is stopped by the discharger for at least an interval corresponding to one revolution of the photoconductive body, thus completing the cycle.
In the apparatus with the above arrangement, a defective image may be formed due to abnormality of a charging means and transfer means, such as a mounting error of the main charger, transfer charger, or the like, mis-contact between the main charger and the transfer charger and their power feeding units, disconnection of a discharging wire of the main charger, or the like. In this case, each time such a defective image is formed, an operator must find it (TOSHIBA LASER BEAM PRINTER TN-7700).
However, with this method, since the operator often leaves the apparatus, especially, the laser printer, he often fails to find any defective image, and many defective images are undesirably formed. An abnormality of the main charger when reversal development is employed causes a defective image, called a solid black image, and a large amount of toner is used. In recent developing units, the photoconductive body is cleaned simultaneously with reversal development. When a developing unit having two functions is used, since a large amount of toner consumed due to a solid black defective image or a large amount of toner which is not transferred due to the abnormality of the transfer means and remains on the photoconductive body overcomes cleaning capability, the cleaning function cannot be satisfactorily effected.